As of Wednesday evening, 116 members of the House of Representatives—18 Democrats among them—have signed a letter to Barack Obama insisting that any strikes against Syria must first be authorized by Congress.

The letter asserts that a strike without Congressional authorization would be unconstitutional. The leader of the group, Rep. Scott Rigell (R-VA), said, “Engaging our military in Syria when no direct threat to the United States exists and without prior congressional authorization would violate the separation of powers that is clearly delineated in the Constitution.”

Rigell wrote that Obama should recall Congress to discuss authorization of any strikes against Syria, saying, “If you deem that military action in Syria is necessary, Congress can reconvene at your convenience.” Congress is in recess until September 9. Rigell also has stated that Obama’s 2011 authorization to use U.S. forces in Libya was unconstitutional.

Rigell released a statement saying, “I’m grateful and encouraged by the strong, bipartisan support this letter has received. It’s a clear indication that this issue is not personal to the president, but rather represents common ground in Congress and a deep respect for the Constitution.”